diff options
Diffstat (limited to 'bcopy32.inc')
| -rw-r--r-- | bcopy32.inc | 128 |
1 files changed, 82 insertions, 46 deletions
diff --git a/bcopy32.inc b/bcopy32.inc index d0f8a462..056f29bd 100644 --- a/bcopy32.inc +++ b/bcopy32.inc @@ -71,6 +71,13 @@ bcopy_gdt: desc TSS dw 104-1, DummyTSS ; 30h 32-bit task state segment dd 00008900h ; present, dpl 0, 104 bytes @DummyTSS + + ; 16-bit stack segment, which may have a different + ; base from DS16 (e.g. if we're booted from PXELINUX) + desc SS16 + dd 0000ffffh ; 38h Data segment, use16, read/write, + dd 00009300h ; present, dpl 0, cover 64K + bcopy_gdt_size: equ $-bcopy_gdt ; @@ -86,13 +93,33 @@ bcopy_gdt_size: equ $-bcopy_gdt ; Outputs: ; ESI - first byte after source (garbage if ESI == -1 on entry) ; EDI - first byte after target -; ECX - zero ; -bcopy: push eax - push ebx - push esi - push edi - push ecx +bcopy: pushad + mov bx,pm_bcopy + call simple_pm_call + popad + add edi,ecx + add esi,ecx + ret + +; +; This routine is used to invoke a simple routine in 16-bit protected +; mode (with 32-bit DS and ES, and working 16-bit stack.) +; Note that all segment registers including CS, except possibly SS, +; are zero-based in the protected-mode routine. +; +; No interrupt thunking services are provided; interrupts are disabled +; for the duration of the routine. Don't run for too long at a time. +; +; Inputs: +; BX - routine to execute +; ECX, EDX, EBP, ESI and EDI passed to the called routine +; +; Outputs: +; EAX, EBX destroyed +; All other registers as returned from called function +; +simple_pm_call: pushf ; Saves, among others, the IF flag push ds push es @@ -102,36 +129,73 @@ bcopy: push eax cli call enable_a20 - mov byte [bcopy_gdt.TSS+5],89h ; Mark TSS unbusy + mov byte [cs:bcopy_gdt.TSS+5],89h ; Mark TSS unbusy - mov bx,ss ; Save the stack segment value! + ; Convert the stack segment to a base + xor eax,eax + mov ax,ss + shl eax,4 + or eax,93000000h + mov [cs:bcopy_gdt.SS16+2],eax + push ss ; Save real-mode SS selector + o32 lgdt [cs:bcopy_gdt] mov eax,cr0 or al,1 mov cr0,eax ; Enter protected mode jmp PM_CS16:.in_pm +.in_pm: + mov ax,PM_SS16 ; Make stack usable + mov ss,ax -.in_pm: mov ax,PM_DS16_4G ; Data segment selector + mov al,PM_DS16_4G ; Data segment selector mov es,ax mov ds,ax - ; Set ss, fs, and gs, in case we're on a virtual machine - ; running on Intel VT hardware -- it can't deal with a - ; partial transition, for no good reason. However, - ; ss is NOT zero in general, so we have to preserve - ; the value. + ; Set fs, gs, tr, and ldtr in case we're on a virtual + ; machine running on Intel VT hardware -- it can't + ; deal with a partial transition, for no good reason. mov al,PM_DS16_RM ; Real-mode-like segment mov fs,ax mov gs,ax - mov ss,ax - mov al,PM_TSS ; Intel VT really doesn't want ltr ax ; an invalid TR and LDTR, so give xor ax,ax ; it something that it can use... lldt ax ; (sigh) + call bx ; Call actual routine + +.exit: + mov ax,PM_DS16_RM ; "Real-mode-like" data segment + mov es,ax + mov ds,ax + + pop bx ; Previous value for ss + + mov eax,cr0 + and al,~1 + mov cr0,eax ; Disable protected mode + jmp 0:.in_rm + +.in_rm: ; Back in real mode + mov ss,bx + pop gs + pop fs + pop es + pop ds + call disable_a20 + + popf ; Re-enables interrupts + ret + +; +; pm_bcopy: +; +; This is the protected-mode core of the "bcopy" routine. +; +pm_bcopy: cmp esi,-1 je .bzero @@ -147,7 +211,7 @@ bcopy: push eax mov cl,al ; Copy any fractional dword a32 rep movsb - jmp .exit + ret .reverse: std ; Reverse copy @@ -166,7 +230,7 @@ bcopy: push eax a32 rep movsd cld - jmp .exit + ret .bzero: xor eax,eax @@ -177,34 +241,6 @@ bcopy: push eax mov cx,si ; Write fractional dword a32 rep stosb - ; jmp .exit - -.exit: - mov ax,PM_DS16_RM ; "Real-mode-like" data segment - mov es,ax - mov ds,ax - - mov eax,cr0 - and al,~1 - mov cr0,eax ; Disable protected mode - jmp 0:.in_rm - -.in_rm: ; Back in real mode - mov ss,bx - pop gs - pop fs - pop es - pop ds - call disable_a20 - - popf ; Re-enables interrupts - pop eax - pop edi - pop esi - add edi,eax - add esi,eax - pop ebx - pop eax ret ; |